1. Field of the Invention
This invention relates to a fixing device and an image forming apparatus.
2. Description of Related Art
In conventional image forming apparatuses such as printers, photocopiers, facsimiles of electrophotographic method, provided are a photosensitive drum, a charge device charging the photosensitive drum to have prescribed polarity and potential, an exposure device forming electrostatic latent images of printing data on the charged photosensitive drum, a development device visualizing the electrostatic latent images with toner as toner images, a transfer device transferring the toner images to printing paper, and a fixing device fixing toner images to the printing paper. With this mechanism, printing of the printing data is performed on the printing paper.
Such a fixing device generally used in the image forming apparatus of the electrophotographic method, has a thermal roller system in which a fixing roller and a pressing roller are rotated as in a pressurized contact state and in which the toner images formed on the printing paper are heated and melt to be fixed upon conveying the printing paper in sandwiching the paper with the fixing roller and the pressing roller. The fixing roller has inside a fixing heater or heaters made of, e.g., a halogen lamp, and is heated with the fixing heater.
With the fixing device having such a structure, however, a warming-up time of a certain period is required to heat up the fixing roller to be at a temperature necessary for fixing step from the room temperature.
A technique has been proposed in which the fixing device is subject to waiting as the fixing heater is maintained at a temperature several degrees (Celsius) lower than the prescribed temperature by controlling turning on and off the fixing heater to make shorter the warming-up time for heating up the fixing roller to be at the temperature necessary for fixing step, until a time starting printing operation of subsequent printing data after completion of fixing the printing of arbitrary printing data to the printing paper (see, e.g., Japanese Patent Application Publication No. 2013-068,906 (A1)).
With such a fixing device, if the printing of the printing data is not performed as being in the waiting state and left as it is for a long time, a deformation or nip scar occurs in a shape extending along the outer diameter of the roller having a harder hardness on a surface of the roller having a softer hardness due to long time pressurized contact between the fixing roller and the pressing roller, so that abnormal noise may occur when the deformation goes by while the fixing roller and the pressing roller rotate, and so that rotation load may be increased.